Ports required for trust relationship:

• 389 (TCP and UDP) – Directory, Replication, User and Computer Authentication, Group Policy, Trusts – LDAP
• 636 (TCP) – Directory, Replication, User and Computer Authentication, Group Policy, Trusts – LDAP SSL
• 3268 (TCP) – Directory, Replication, User and Computer Authentication, Group Policy, Trusts – LDAP GC
• 3269 (TCP) – Directory, Replication, User and Computer Authentication, Group Policy, Trusts – LDAP GC SSL
• 88 (TCP and UDP) – User and Computer Authentication, Forest Level Trusts – Kerberos
• 53 (TCP and UDP) – User and Computer Authentication, Name Resolution, Trusts – DNS
• 445 (TCP and UDP) – Replication, User and Computer Authentication, Group Policy, Trusts – SMB,CIFS,SMB2, DFSN, LSARPC, NbtSS, NetLogonR, SamR, SrvSvc

Reference:

• https://technet.microsoft.com/en-us/library/dd772723(v=ws.10).aspx
  https://support.microsoft.com/en-us/help/179442/how-to-configure-a-firewall-for-domains-and-trusts